What if you have more than one argument in you callback. Unfortunately Completer will not help you here, you still need to write this tiring code from the first example. But how often do you have multiple arguments in your callbacks? One workaround is to wrap all of them into a helper class… This is your design choice…

Have you knew about Completer before? Did you used it already? Are you going to use this pattern in your tests? I’m looking forward for your answers in comment section.